Infection of mammals with mycobacteria other than tubercle bacilli is responsible for certain cross reactions to PPD-type tuberculins prepared from culture filtrates of metabolically "old" mycobacteria. Realizing the greater specificity of antigens derived from the proto- plasm of young, actively growing mycobacterial cultures, this project proposes to fractionate low molecular weight peptide or glycopeptide sensitins from the protoplasm of mycobacteria. Protoplasmic extracts will be prepared from cells disrupted both by Ribi pressure cell and Parr nitrogen cell-disruption bomb. Extracts will be purified by a combination of differential centrifugation, chemical fractionation and molecular seive chromatography. Results of pilot studies indicate that these sensitins have specificity superior to currently available products. In addition to their use as skin test antigens for the specific in situ identification mycobacterial pathogens, these peptides also may be useful in serotyping mycobacteria and for sero-diagnosis of mycobacterioses in man and lower animals.